A high temperature gas cooled reactor is a high temperature reactor in which graphite serves as a moderator and helium serves as a coolant, and is an advanced nuclear reactor with a good inherent safety, high electricity generating efficiency and a very wide range of application fields. The graphite dust produced by the graphite materials or fuel elements located inside the high temperature gas cooled reactor due to abrasion is radioactive. These tiny graphite dust mainly disperse in a circuit helium space in the form of aerosol. It is well known that the helium has a strong permeability in comparison with other mediums, thus one of the important applications thereof in the industrial field is seal leak detection. The pressurized helium flowing through the core of a reactor carries radioactive graphite dust. As a result, the helium also has a certain amount of radioactivity; therefore, it is necessary to take strict sealing measures for the pressure boundary and auxiliary system pipelines of a high temperature gas cooled reactor. If external leakage occurs in the equipment and pipeline attachments of these systems, not only are the normal operation and safe shutdown of the reactor affected, but the safety of operators and the environment are endangered. On the other hand, if a leak occurs, it will also result in economic waste because the price of helium itself is expensive.
In order to avoid a helium leak, the connection of equipment, valves, pipelines and pipe fittings in a high temperature gas cooled reactor mainly use a welded structure, or a sealing structure with edge-sealing welding. For example, all the helium valves in a HTR-10 experimental reactor adopt a structure by using a corrugated pipe with filler sealing between the valve cap and the valve rod. In spite of this, a large number of pressure-bearing mechanical devices that includes moving parts are located in the pipelines of a circuit pressure boundary and reactor auxiliary system, requires using methods such as power-driven or electromagnetism, etc. for remote operation, and the driving mechanism thereof must ensure reliable operation under the environment of on-site irradiation, temperature and humidity. For these pressure-bearing mechanical devices, if a filler or packing seal is adopted, it is difficult to radically solve the problem of a helium seal because a seal surface exists. Because of the inherent flexibility of the corrugated pipe, it has little rigidity, is liable to be unstable, unable to reverse at large angles and limited in fatigue life, which is difficult to meet the technical requirements for the operations such as large torque, continuous operation for a long time, reciprocating rotation and frequent start and stop, etc. by means of a corrugated pipe for sealing.
In order to solve the problem of reliable sealing to the radioactive helium by pressure boundary operation mechanical devices, high temperature gas cooled reactors that have been built or under construction mainly adopt an inclusion structure with a motor-driven or electromagnetism driving mechanism inside the pressure-bearing casing, such as the non-active safety drive device applied in the absorber ball shutdown system of a high temperature gas cooled reactor as disclosed in the description of Chinese patent publication No. CN 101159172A, and a centrifugal helium compression of a pebble-bed high temperature gas cooled reactor as disclosed in CN 101109390A. If the inclusion structure is adopted, the mechanical dynamic seal of operational components is transformed into a static seal of electrical penetration assemblies. Although the problem of helium leakage is solved by this way, a series of technical problems about the harsh environment inside the pressure-bearing casing and the reliable operation requirements such as the issues of anti-radiation, temperature tolerance, pressure-bearing, lubrication and abrasion, operation for a long period of time, etc. with respect to the driving motor and the transmission member also must be solved. Therefore, the driving motor and the transmission member must adopt non-standard designs and be subjected to engineering tests. On the other hand, the electrical penetration assemblies in the nuclear plant are generally customized with respect to specific types of reactors and special pressure boundary safety and equipment (e.g. patent publication No. CN1176469C). The cost of electrical penetration assembly customization or the pressure-bearing mechanical equipments research based on different structures and operational environments is quite high, which is unacceptable for the non-safety level pressure-bearing mechanical equipment of the auxiliary system. Thus generally it only adopts electric connectors with low reliability. This kind of normal electric connectors and its connecting parts for connecting with the pressure-bearing casing may therefore become a weak link of the pressure-bearing mechanical equipment.